DYNAMIC LIGHT-SCATTERING IN POLYMER-DISPERSED LIQUID-CRYSTALS

A polymer dispersed liquid crystal was studied by dynamic light scatte ring. In the experiments, where no electric field is applied, the syst em exhibits additional slow dynamics to the ones observed in bulk nema tic liquid crystals. This slow dynamics gradually disappears with an i ncreasing electric field. While the measured time intensity con elatio n function does not depend on the scattering vector in the system wher e no held is applied due to the multiple scattering, its dependence on the electric held shows expected size effects. In confined systems, w ith typical size d, there are no eigenmodes of the orientational fluct uations in droplets with the wave vectors less than the minimal wave v ector q(min) similar to pi/d. We observed a quadratic dependence of th e inverse relaxation time on the scattering vector down to a certain s cattering vector, below which the relaxation time remains constant. Th e size calculated from this minimal scattering vector is in agreement with the average droplet size obtained from scanning electron microsco pe photographs and the atomic force microscope images of our sample. T he electric field changes the temperature behavior of the inverse rela xation time near the nematic-isotropic phase transition, which increas es with the temperature when the electric field is applied, but decrea ses when the field is absent.